Layer-by-layer (LbL) assembly is a conformal coating “platform” technology capable of imparting a multiplicity of functionalities on nearly any type of surface in a relatively environmentally friendly way. At its core, LbL is a solution deposition technique in which layers of cationic and anionic materials (e.g. nanoparticles, polymers and even biological molecules) are built up via electrostatic attractions in an alternating fashion, while controlling process variables such as pH, coating time, and concentration. Here we are producing nanocomposite multilayers (50-1000 nm thick), having 10-96 wt % clay, that are completely transparent and exhibit oxygen transmission rates below 0.005 cm3/m2·day. Phosphorus and nitrogen-rich molecules can also be used to impart intumescent behavior. These multilayer assemblies are very conformal and able to impart flame resistance to highly flammable woven and nonwoven fabric substrates without altering other beneficial properties intrinsic to the fibers themselves (strength, breathability, etc.). Nylon-cotton and polyester-cotton blends have passed standard vertical flame tests (ASTM D6413) with 12-18 wt % coating deposited. Similar nanocoatings produced with graphene and carbon nanotubes have a surprisingly high Seebeck coefficient (> 100 mV/K) and exhibit very high thermoelectric power factor (up to 3000 mW/m·K2). We hope to eventually produce fabric that can generate voltage from body heat. Our work in these areas has been highlighted in C&EN, ScienceNews, Nature, Smithsonian Magazine, Chemistry World and various scientific news outlets worldwide.

Novel vinyl ether monomers were produced from a variety of compounds that can be obtained from renewable resources, such as plant oils, lignin decomposition products, and essential oils. Using an appropriate cationic polymerization system, novel linear homopolymers and copolymers were produced that retained double bonds derived from the renewable resource. This unsaturation was utilized to provide crosslinked networks either directly or through derivatization of the double bonds. Select polymer compositions were shown to provide substantial utility for a variety of applications including paints and coatings, personal care products, ground water remediation, and rubber compounds. This presentation will provide an overview of the chemistry and potential applications associated with this technology platform.

Special MNT Seminar - Monday, September 26, 2016, 3:00, 148 R1

New Hybrid Materials Based on Element-Blocks, Professor Yoshiki Chujo, Department of Polymer Chemistry, Kyoto University

We recently proposed the idea of polymeric materials based on “element-blocks” or structural units consisting of various groups of elements. This is a new concept for hybrid materials that can be expected to promote new research and ideas in materials design involving all elements in the periodic table. In this talk, we show the concept of “element-block polymers” with several examples from our recent work. As a representative element block, we select boron dipyrromethene (BODIPYs) dyes, o-carborane, polyhedral oligomeric silsesquioxane (POSS) derivatives and illustrate their roles in the material properties. Initially, electric and optical functional materials are illustrated with the organoboron element blocks. The electron-transport (ET) materials and the aggregation-induced emission (AIE)-active materials are introduced based on BODIPY dyes and o-carborane, respectively. Next, the recent works for evolving organic-inorganic hybrids are demonstrated. By regarding POSS as an inorganic element block, the organic-inorganic hybrid gels were prepared and applied for the bio-relating materials. The superior properties of the POSS-containing hybrid dendrimers for the molecular recognition are presented.

Past MNT Seminars

On How Being Soft and Squishy Affects Phase Behavior: The Case of Charged-Microgel Suspensions, Professor Alberto Fernandez-Nieves, School of Physics, Georgia Institute of Technology

Microgels are an interesting class of mesoscopic soft particles that can deform and compress. When suspended in a solvent at large number density, they are able to crystallize and form glasses. However, for microgels, this depends on single-particle stiffness. We will discuss recent results with charged microgel particles with different stiffness. We will first show that the suspension osmotic pressure is controlled by those counterions in solution that are able to escape from the electrostatic attraction exerted by the microgel particles. We will then exploit this fact to obtain the particle volume fraction, f, and the microgel volume as a function of particle concentration, even in highly overpacked states, where the particles are forced to both change shape and compress. In terms of f, we find that the width of the fluid-crystal coexistence region decreases with decreasing microgel stiffness to eventually disappear for sufficiently soft microgels; in these cases, the suspensions remains fluid-like at all explored concentrations. By comparing our results with expectations from computer simulations, we propose possible interparticle-interactions that could potentially capture our experimental observations.

The structure of the electrical double layer has been debated for well over a century, since it mediates colloidal interactions, regulates surface structure, controls reactivity, sets capacitance and represents the central element of electrochemical supercapacitors. The surface potential of such surfaces generally exceeds the electrokinetic potential, often substantially. Traditionally, a Stern layer of non-specifically adsorbed ions has been invoked to rationalize the difference between these two potentials; however, the inability to directly measure the surface potential of dispersed systems has rendered quantitative measurements of the Stern Layer potential, and other quantities associated with the Outer Helmholtz Plane, impossible. Here we describe our development of X-ray photoelectron spectroscopy (XPS) from a liquid microjet to measure the absolute surface potentials of silica nanoparticles dispersed in aqueous electrolytes. We quantitatively determine the impact of specific cations (Li+, Na+, K+, and Cs+) in chloride electrolytes on the surface potential, the location of the shear plane and the capacitance of the Stern layer. We find that the magnitude of the surface potential increases linearly with hydrated cation radius. Interpreting our data using the simplest assumptions and most straightforward understanding of Gouy-Chapman-Stern theory reveals a Stern layer (bounded by the Outer Helmholtz Plane) whose thickness corresponds to a single layer of water molecules hydrating the silica surface, plus the radius of the hydrated cation. We describe a modified Poisson-Boltzmann (PB) model that adds hydration repulsion between counterions to their Coulomb interaction. While retaining much of the simplicity of the classical PB model, this modified model predicts surface potentials and Stern layer thicknesses for the different counterions that are in excellent agreement with the experiments.

Mixed Valence State Nanoceria and it's Role in Angiogenesis, Professor Sudipta Seal, Pegasus Professor and University Distinguished Professor, Director of AMPAC and NanoScience Technology Center (NSTC), University of Central Florida

Angiogenesis is the formation of new blood vessels from existing blood vessels and is critical for many physiological and pathophysiological processes. In this study we have shown the unique property of redox active nanoparticles (Re-NPs) to induce angiogenesis, observed using both in vitro and in vivo model systems. In particular, Re-NPs trigger angiogenesis by modulating the intracellular oxygen environment and stabilizing hypoxia inducing factor 1alpha endogenously. Furthermore, correlations between angiogenesis induction and Re-NPs physicochemical properties including: surface valence state ratio, surface charge, size, and shape were also explored. High surface area and mixed valence states make these nanoparticles more catalytically active towards regulating intracellular oxygen, which in turn led to more robust induction of angiogenesis. Atomistic simulation was also used, in partnership with in vitro and in vivo experimentation, to reveal that the surface reactivity of NPs and facile oxygen transport promotes pro-angiogenesis. (This research is funded by USA National Science Foundation and National Institute of Health) At the end, I will conclude the talk describing our research activities at Materials and Nano Center at UCF.

Ultra-Resolution Photoluminescence Spectroscopy and Electron Microscopy to Probe the Spatial Distribution of Emitted Photons from Semiconductor Nanocrystalline Higher Order Structures, Professor Alan Van Orden, Department of Chemistry, Colorado State University

This presentation will report new techniques to investigate excited state electronic energy transport in semiconductor nanocrystalline quantum dot (QD) higher order structures, from small aggregates to macroscopic thin films. QDs have attracted considerable scientific interest because of their unique size-tunable optical and electronic properties, and their ability to be used as nanometer scale building blocks in a broad range of optoelectronic devices and biological labelling applications. In many cases, a large ensemble of quantum dots must be organized into higher order structures. QD higher order structures have characteristic optical properties that are distinct from isolated QDs, due to the ability of the QDs to interact with each other through electronic coupling and/or energy transfer. Researchers attempting to characterize or model this coupling normally must rely on spectroscopic information that averages over large ensembles of QDs. However, the coupled QDs often exist in heterogeneous surroundings, with wide variations in cluster sizes, interparticle spacings, and local environments. Thus, ensemble averaging techniques have a limited ability to uncover the detailed interactions involved in the coupling. Furthermore, ensemble methods do not have the ability to investigate the single molecule dynamics of the QDs, or the impact of these dynamics on the optical and electronic properties of the higher order structures. To overcome these limitations, we have developed novel super-resolution imaging microscopy techniques to spatially resolve the photoluminescence coming from individual QDs within higher order structures. We have also developed novel methods to spatially correlate the super-resolution imaging data with ultra-resolution scanning and transmission electron microscope images. Using these techniques, we can trace the energy transport pathways among the QDs and precisely measure, with sub-nanometer precision, the QD sizes, structural arrangements, inter-QD distances, and crystal lattice orientations. We are using these combined methods to investigate the intricate relationships between structure, electronic energy transport, and function in these important systems.

Enzymatic reactions are traditionally studied at the ensemble level, despite significant static and dynamic inhomogeneities. Subtle conformational changes play a crucial role in protein functions, and these protein conformations are highly dynamic rather than being static. We applied single-molecule spectroscopy to study the mechanisms and dynamics of enzymatic reactions involved with kinase and lysozyme proteins. Enzymatic reaction turnovers and the associated structure changes of individual protein molecules were observed simultaneously in real-time by single-molecule FRET detections. We obtained the rates for single-molecule conformational active-site open-close fluctuation and correlated enzymatic reactions. Our new approach is applicable to a wide range of single-molecule FRET measurements for protein conformational changes under enzymatic reactions and protein-protein interactions in cell signaling. Using this approach, we analyzed enzyme-substrate complex formation dynamics to reveal (1) multiple intermediate conformational states, (2) conformational motions involving in active complex formation and product releasing from the enzymatic active site, and (3) conformational memory effects in the chemical reaction process. Furthermore, we have applied AFM-enhanced single-molecule spectroscopy to study the mechanisms and dynamics of enzymatic reactions. We obtained the rates for single-molecule conformational active-site open-close fluctuation and correlated enzymatic reactions. We have demonstrated a specific statistical analysis to reveal single-molecule FRET anti-correlated fluctuations from a high background of fluorescence correlated thermal fluctuations. Our new approach is applicable to a wide range of single-molecule AFM-FRET measurements for protein conformational changes under enzymatic reactions, including AFM-FRET control of enzymatic reactivity by mechanical-force manipulating protein conformations.

Determination of the mechanical response of polymeric materials with dimensions less than 100 nm is a continuing challenge. Here we describe a novel membrane (“nano-bubble”) inflation method we have developed for the purpose of making measurements of the creep response of ultrathin polymer films and show two major findings. The first is that the material dynamics as measured by the creep response of the membranes depends dramatically on film thickness. For example, in polystyrene films, the dynamics is accelerated so much that the glass transition temperature of a 11 nm thick film is reduced by approximately 50 K relative to the macroscopic value. Furthermore, we have discovered that the nominal rubbery plateau in ultrathin films is stiffened by upwards of two orders of magnitude relative to the macroscopic state and the rate of stiffening (stiffening index S) correlates with the shape of the segmental relaxation in accordance with a recent model proposed by Ngai, Prevosto and Grassia. We have elaborated this finding further and observe a strong correlation with the fragility index m that is related to glass formation according to the Angell categorization of super cooled liquids. These results will be discussed in terms of current understanding of the impact of nanoconfinement on the glass transition behavior of polymers. In addition to being able to characterize the creep response of the ultrathin polymer films, we have also succeeded in adapting the bubble inflation method to make measurements on a graphene/polymer nano-sandwich structure and show that the method can be used to not only extract the stiffness of the graphene inner layer of the composite but that the method can be used to extract the interfacial shear strength of the polymer-graphene couple.

Photo-induced charge transfer at the interface of two materials is a fundamental process in (i) photovoltaic and (ii) photocatalytic applications. The photo-induced time-dependent electron dynamics are computed for different interfaces by a combination of ab initio electronic structure and time-dependent density matrix methodology. A dissipative equation of motion for the reduced density matrix for electronic degrees of freedom is used to study the phonon-induced relaxation of hot electrons in the simulated systems. Non-adiabatic couplings between electronic orbitals are computed on-the-fly along nuclear trajectories. Equations are solved in a basis set of orbitals generated ab initio from a density functional. For an application to photovoltaic effect, one explores light-induced electric current in a model of a simplified photovoltaic cell composed of a Si nano-crystal co-doped with p-and n- type doping, interfacing with Au electrodes. Charge carrier dynamics induced by selected photo-excitations show that hole relaxation in energy and in space is much faster than electron relaxation. Use of the continuity equation for electric current allows us to identify substantial local currents at the Si/Au interfaces and small overall net charge transfer across the slab. For an application to photocatalytic water splitting, charge transfer dynamics is explored at the interface of supported metal nanocluster and liquid water. The metal cluster introduces new states into the band gap of semiconductor TiO2 surface, narrows the band gap of TiO2, and enhances the absorption strength. The H2O adsorption significantly enhances the intensity of photon absorption, which is due to the formation of metal-oxygen (water) coordination bonds at the interfaces. The metal cluster promotes the dissociation of water, facilitates charge transfer, and increases the relaxation rates of holes and electrons. Reported results help in understanding basic photophysical and protochemical processes contributing to harvesting solar energy by photovoltaics and photoelectrochemical water splitting.

When one folds a thin solid film that is only a few atoms thick, such as graphene, the film properties can be controlled for various functions. For example, a simple compression of the folded film can change optical, electrical, wetting and adhesion characteristics of the film, and can be used for making multifunctional materials such as transparent electric circuits, self-cleaning surfaces, oil-spill cleaning cloths and self-adjusting friction grips. Such atomic-layer nanostructures can be folded and self-organized by nonlinear large deformation of soft material substrates. In particular, nano science and technology has enabled us to explore new functional properties of hierarchically ruga-structured materials through folding or wrapping thin atomic-layer structures with nanometer scale features. The Latin word ruga means a state of a “large-amplitude” wrinkle, crease, fold or ridge to form various 1-D or 2-D patterns. As multi-scale surface morphologies of rugae determine effective properties such as wetting, adhesion, friction, flexoelectric and optoelectronic properties, ruga state control is considered as a viable method for real-time regulation of effective material properties. It is found that graded or layered elastic properties of the substrate can provide diverse bifurcation paths of the attached atomic-layer deformation under lateral compression, producing various atomic-layer ruga states. Nonlinear mechanics of soft-material substrate enables us to construct ruga-phase diagrams. As an example, a mathematical analysis of sequential bifurcation processes of hyper-elastic neo-Hookean substrates is used to construct generic ruga-phase diagrams. When an atomically layered structure such as multi-layer graphene is folded by ruga control, nano-scale crinkles are generated. In general, nano-scale crinkle ridges are invisible to conventional AFM due to its peculiar flexoelectric properties. Here, a new invention of “Dual-Tip AFM Interferometer” (DT-AFMI) will be introduced, which makes the invisible visible. The DT-AFMI image reveals that the crinkle ridge of a multi-layer graphene has its ridge width less than 1.8nm. The nano-crinkle ridges have strong flexoelectric characteristics, and the crinkle ridge networks of the top graphene layer exhibit high molecular adsorptivity. Potential applications of such high molecular adsorptivity localized along the nano-ridges will be discussed as well.

Encapsulation of Solutes in Lipid Vesicles: Origins of Life Considerations, Dr. Tereza Pereira de Souza, Rowland Institute, Harvard University

In the past years we have investigated the entrapment of macromolecules inside vesicle by analyses of cryo-transmission electron microscopy of liposome populations created in the presence of ferritin, ribosomes and small macromolecular aggregates. And surprisingly, results reveal that the local (intra-liposomal) macromolecules concentration in these liposomes largely exceeds the bulk concentration. This seminar aims to summarize and discuss these results under the light of the origins of life scenario and synthetic biology, addressing question as: What is the minimal size of a minimal cell? Is the number of entrapped macromolecules inside vesicles homogeneous? Lipid compartments are frequently addressed as agents of confinement and protection, but could these compartments have a more active role in the pre-biotical scenario? In another words, does the formation of lipid compartments play a role in concentrating the "entrapped to be" macromolecules?

Special MNT Seminar - Monday, November 10, 2014, 3:30, Sudro 27

Transdermal Therapeutic Systems (TTS) have made their way over the last decades as an alternative to oral formulations not only for circumvention of the first pass effect as for example delivering nitroglycerine, but also for maintaining steady plasma level values and for reducing serious side effects during therapy. A very good example for the latter case is the Exelon TTS(r) with its active ingredient rivastigmine, which is used in therapies against Alzheimer's disease.

Collective motion is one of the simplest forms of self-organization in systems of active components such as cell colonies, bird flocks, fish schools, or groups of autonomous robots. Its emergence in fluid-like swarms with aligning interactions has been the focus of much research activity. In this talk, I will introduce a different model for collective motion, consisting of self-propelled particles connected by linear springs without explicit aligning dynamics. In this system, a simple elasticity-based mechanism drives the particles to self-organize by cascading self-propulsion energy towards lower-energy modes. Given its ubiquity, this mechanism could play a relevant role in various natural and artificial swarms.

We present examples from our group where biophysics impacts unsolved medical problems. We start with bacterial biofilms, which are structured multi-cellular communities that are fundamental to the biology and ecology of bacteria. The first step in biofilm formation, adaptation to life on a surface, requires the coordination of biochemical signaling, polysaccharide production, and molecular motility motors. These crucial early stages of biofilm formation are at present poorly understood. By adapting tracking algorithms from colloid physics, we dissect bacterial social behavior at the single cell level. We will also discuss how we can learn from innate immunity peptides, and renovate antibiotic design via the biophysics of peptide-membrane interactions. Finally, we examine the pathological role of antimicrobial peptides in autoimmune diseases.

Making Non Stick Coatings out of Thin Air, Professor Robert Lamb, Canadian Light Source Inc. Canada &The University of Melbourne Australia

Non stick coatings are everywhere in nature and these have stimulated numerous practical applications. For example leaf surfaces have been the inspiration for novel waterproof textile coatings. Insect wings may hold the key to strategies for antifouling on marine vessels and the associated energy savings that go hand in hand with such developments. The latest “green” nanotechnology approach to fabricating extremely non stick surfaces involves self-organized and chemically cross linked nanoparticles. These generate exceptionally rough multi scale hierarchical interfaces that simultaneously possess a unique ability to self-clean themselves. But what is behind such an effect? Why does a lotus leaf stay clean in nature but when freshly cut it rapidly contaminates? Washing inert “dirt” from textiles is enhanced if the surface has multi scale roughness yet biological (live) contaminants “sense” subtle nanoscale features and may “hold on” despite such rinsing. Furthermore what are the requirements to turn such a curiosity into a practical technology? Shining the bright light of a synchrotron on the problem may be the answer.

Block copolymers belong to a broad class of amphiphilic compounds that includes soaps, lipids and nonionic surfactants. These macromolecules assemble into micelles with molecular dimensions on the order of 5 to 50 nm in size when mixed with excess solvent that preferentially solvates one block type. This presentation will explore two different aspects of block copolymer micelle formation.The fundamental thermodynamic and kinetic factors that control micelle shape and dynamics will be discussed based on small-angle x-ray and neutron scattering (SAXS and SANS) experiments and cryogenic transmission and scanning electron microscopy results. Although the structural features displayed by amphiphilic block copolymers resemble those associated with the self-assembly of lipids and simple surfactants (e.g., spherical and cylindrical micelles and vesicles) a macromolecular architecture leads to remarkably different dynamic properties, linked to a vanishingly small critical micelle concentration. As a consequence, molecular exchange is rapidly extinguished with increasing molecular weight resulting in non-ergotic behavior. These concepts have been exploited in developing a recently commercialized technology that provides immense improvements in the fracture toughness of thermosetting epoxy plastics, which also will be described.

Drug-delivery depends crucially on the ability to translocate drugs across the cell membrane. While some drugs do this naturally, most of the promising new therapies require a vehicle (or vector) that will deliver the drugs into the cytosol. Such is the way also how natural infections work. In this talk I will introduce a new counterintuitive way to bypass the membrane by exploiting fusion pathways. This work is inspired by the recent discovery that a particular class of nanoparticles can enter the cell through non-endocytotic pathways without disrupting the membrane. These nanoparticle are composed of Au protected with a multi component ligand shell. Such nanoparticles essentially behave a “nano chamaleons” altering on-the-fly their surface chemistry to mimic that of the membrane. I will discuss the origins of such behavior and uncover the pathway by which such nanoparticles enter cells. In particular, I will explain in detail how one can control the interfacial properties of the nanoparticle and potentially target different membrane compositions. These nanoparticles can mimic several different functions performed by membrane proteins such as fusion proteins and lipid shuttling proteins, opening new possibilities in delivering drugs, as well as serving as artificial proteins themselves. Thus, understanding and controlling such a system can potentially be utilized in a wide variety of fields.

Nanocrystals exhibit a wide range of unique properties (e.g., electrical, optical, and optoelectronic) that depend sensitively on their size and shape, and are of both fundamental and practical interest. Breakthrough strategies that will facilitate the design and synthesis of a large diversity of nanocrystals with different properties and controllable size and shape in a simple and convenient manner are of key importance in revolutionarily advancing the use of nanocrystals for a myriad of applications in lightweight structural materials, optics, electronics, photonics, optoelctronics, magnetic technologies, sensory materials and devices, catalysis, drug delivery, biotechnology, and among other emerging fields. In this talk, I will elaborate a general and robust strategy for crafting a large variety of functional nanocrystals with precisely controlled dimensions (i.e., plain, core/shell, and hollow nanoparticles) by capitalizing on a new class of unimolecular star-like block copolymers as nanoreactors. This strategy is effective and able to produce organic solvent-soluble and water-soluble monodisperse nanoparticles, including metallic, ferroelectric, magnetic, luminescent, semiconductor, and their core/shell nanoparticles, which represent a few examples of the kind of nanoparticles that can be produced using this technique. The applications of these functional nanocrystals in energy-related applications (i.e., solar cells and photocatalysis) will also be discussed.